1. Field of the Invention This invention relates to compositions containing asphalt and polyolefins and is particularly concerned with improved compositions prepared by blending asphalt and a reject polypropylene which contains a mixture of atactic and isotactic polypropylene and includes inorganic salts and other residues from the polypropylene manufacturing process.
2. Description of the Prior Art
Conventional methods for the manufacture of polypropylene generally involve stereospecific polymerization of the propylene monomer in the presence of a catalyst containing a coordination complex of a transition metal halide and an aluminum alkyl or similar organometallic compound. The product from this reaction is a slurry of polypropylene and catalyst in a hydrocarbon diluent. A low molecular weight alcohol is normally added to this slurry to quench the reaction, precipitate crystalline or isotactic polypropylene, and solubilize the catalyst. Amorphous or atactic polypropylene remains in solution in the diluent. Subsequent steps of the process generally involve recovery of the precipitated isotactic polypropylene, neutralization of the active catalyst, and recovery of the alcoholic solution and hydrocarbon diluent. The isotactic polypropylene is normally recovered as a high purity polymer suitable for use in a wide variety of coating, casting and molding applications. The atactic polypropylene can be recovered from the remaining residue as an odorless, off-white, tacky thermoplastic material. Although at one time this material was of no commercial importance, it is now widely used as a hot-melt adhesive compounding agent. Since only about 10% of the total polypropylene product consists of the atactic polymer. this material is in very short supply.
The residue resulting from the process described above normally includes the inorganic salts used as the catalyst, color bodies and the like, and significant quantities of atactic and isotactic polypropylene. This material is generally referred to as "reject polypropylene". It normally contains a mixture of atactic and isotactic polypropylene and up to about 20% by weight of inorganic salts. Some water may be present and lesser quantities of solvent may also be included. The polypropylene component may comprise from 5 to about 95% atactic polypropylene and from 95 to about 5% isotactic polypropylene. Typically, the solid constituents may include about 45 weight percent atactic polypropylene, about 45% isotactic polypropylene and about 10% inorganic salts. Heretofore this material has been treated as a waste product. The presence of both atactic and isotactic polypropylene and the salts and other impurites contained in the material have precluded its use in applications for which polypropylene is conventionally employed.